This invention relates to a color display apparatus, more particularly to a color display apparatus with two interfaces.
It is common for the color displays connected to personal computers and similar equipment to receive red, green, and blue video signals on separate signal lines. The method of input of the horizontal and vertical synchronizing pulses, however, has not been standardized. In one system two additional signal lines are provided for input of these synchronizing pulses. In another system the synchronizing pulses are superimposed on one or more of the red, green, and blue video signals. The first system will be called the separate-sync system; the second system will be called the superimposed-sync system.
The two systems require different signal processing circuits in the color display apparatus. A signal processing circuit for the superimposed-sync system must be able to extract the synchronizing pulses from the video input. A signal processing circuit for the separate-sync system must be able to receive the synchronizing pulses via separate signal lines. To provide compatibility with both systems, some color displays incorporate both types of signal processing circuits. These color displays customarily have a manual switch for selecting one of the two signal processing circuits and disabling the other, so that electrical noise at the input terminals for the unused circuit will not interfere with the display.
A manual switch capable of switching high-frequency video signals, however, adds significantly to the cost of the color display apparatus. Furthermore, it is inconvenient for the user to have to set the switch when connecting the display, and if the switch is set to the wrong position by mistake, the display will not work.